Plastic has taken the place of other materials in a variety of industries. Because plastic can be engineered to not shatter, rust or rot, plastic articles have replaced glass, metal and wood articles in many applications. For example, in the food and packaging industries, plastic has replaced glass to minimize breakage, reduce weight, and reduce energy consumed in manufacturing and transport.
Additives are often added to a plastic to facilitate the processing or performance of that material. Commonly used additives are slip agents, which act as an internal lubricant for the polymer during processing. For instance in film processing, slip additives lessen friction between the polymer film and high speed processing and packaging equipment.
Slip additives often function by migrating (i.e., “blooming”) to the surface of the polymer, where they provide a coating that reduces the surface's coefficient of friction. Because the additive is concentrated at the surface where it is needed for processing, less slip additive is required in the polymer material overall.
Contrariwise, other additives can alter the surface of the polymer to make hydrophobic an otherwise hydrophilic polymer surface. Xiong et al. report in “Hydrophobic Modification of Poly(Ethylene Terephthalate) with Epoxy-Modified Polysiloxane by Reactive Extrusion” published in Journal of Macromolecular Science, Part B: Physics (630-641, February 2012) that hydrophobicity of the polyester (polyethylene terephthalate or PET) surface with an increase in water contact angle, even after solvent washing of the surface. But also, Xiang et al. reported that the surfaces of the hydrophobic-modified PET films to be rougher than unmodified PET, an unacceptable result for industrial production of PET films.